EIGRP

ROUTING PROTOCOLS AND CONCEPTS – CHAPTER 9

SANDRA COLEMAN, CCNA, CCAI

INTRODUCTION (PURPLE TEXT IS IMPORTANT)

EIGRP CHARACTERISTICS• Distance vector routing protocol

• Supports classless routing

• Supports VLSM

• Released in 1992

• Cisco proprietary (as is IGRP)

• DUAL algorithm – (Diffusing Update Algorithm)

• RTP (Reliable Transport Protocol) – provides reliable/unreliable delivery of EIGRP packets

EIGRP

Reliable Transport Protocol (RTP)

• Purpose of RTP

–Used by EIGRP to transmit and receive EIGRP packets

• Characteristics of RTP

–Involves both reliable & unreliable delivery of EIGRP packet

Reliable delivery requires acknowledgment from destination

Unreliable delivery does not require an acknowledgement from destination

–Packets can be sent

Unicast

Multicast

–Using address 224.0.0.10

EIGRPEIGRP’s 5 Packet Types

• Hello packets – mulicast packets, reliable delivery

–Used to discover & form adjacencies with neighbors

EIGRP• Update packets –

Uni- or Multicast

–Used to propagate routing information

–Sent only when necessary and only to the routers who need it

• Acknowledgement packets - unicast

–Used to acknowledge receipt of update, query & reply packets

EIGRP • Query & Reply packetsUsed by DUAL for searching for networks

Query packets

• -Can be Unicast or Multicast

Reply packet

• -Use only unicast

EIGRP• Purpose of Hello Protocol

–To discover & establish adjacencies with neighbor routers

• Characteristics of hello protocol

–Time interval for sending hello packet

Most networks it is every 5 seconds Multipoint non broadcast multi-

access networks–Unicast every 60 seconds

-Holdtime

This is the maximum time router should wait before declaring a neighbor down

Default holdtime

–3 times hello interval

EIGRPEIGRP Bounded Updates

• EIGRP only sends update when there is a change in route status. These are sent as unicast packets to the appropriate router interface that needs them.

• Partial update–A partial update includes only the route information that has changed – the whole routing table is NOT sent

• Bounded update–When a route changes, only those devices that are impacted will be notified of the change

• EIGRP’s use of partial bounded updates minimizes use of bandwidth

EIGRPDiffusing Update Algorithm (DUAL)

–Purpose

• EIGRP’s primary method for preventing routing loops

–Advantage of using DUAL

• Provides for fast convergence time by keeping a list of loop-free backup routes

• Administrative Distance (AD)

–Defined as the trustworthiness of the source route

• EIGRP default administrative distances

–Summary routes = 5

–Internal routes = 90

–Imported routes = 170 – learned externally

EIGRP

Authentication

• EIGRP can

– Encrypt routing information

– Authenticate routing information

EIGRP

Network Topology

• Topology used is the same as previous chapters with the addition of an ISP router

ISP is represented

by a loopback address

EIGRP• EIGRP will automatically summarize routes at classful

boundaries

BASIC EIGRP CONFIGURATION

• Autonomous System (AS) & Process IDs–This is a collection of networks under the control of a single authority (reference RFC 1930)

–AS Numbers are assigned by IANA (they also assign IP addresses)

–Entities needing AS numbers ISP

Internet Backbone providers

Institutions connecting to other institutions using AS numbers

BASIC EIGRP CONFIGURATION

• EIGRP autonomous system number actually functions as a process ID

• Process ID represents an instance of the routing protocol running on a router

• Although it is called AS# by Cisco, actually has nothing to do with the AS previously discussed.

• ExampleRouter(config)#router eigrp autonomous-

system

BASIC EIGRP CONFIGURATIONThe router eigrp command

• The global command that enables eigrp is

•router eigrp autonomous-system

•-All routers in the EIGRP routing domain must use the same process ID number (autonomous-system number) Most likely reason PCs can’t talk across routers is that these numbers are NOT identical.

BASIC EIGRP CONFIGURATION

The Network Command

• Functions of the network command–Enables interfaces to transmit & receive EIGRP updates

–Includes entire network or subnet in EIGRP updates

• Example–Router(config-router)#network network-address

WILDCARD MASKS

• By default, when using the network command and a classful network address such as 172.16.0.0, all interfaces on the router that belong to that classful network address will be enabled for EIGRP.

• However, there may be times when the network administrator does not want to include all interfaces within a network when enabling EIGRP.

• To configure EIGRP to advertise specific subnets only, use the wildcard-mask option with the network command

BASIC EIGRP CONFIGURATION• The network Command with a Wildcard Mask

• Think of a wildcard mask as the inverse of a subnet mask. The inverse of subnet mask 255.255.255.252 is 0.0.0.3. To calculate the inverse of the subnet mask, subtract the subnet mask from 255.255.255.255:

• Router(config-router)#network network-address [wildcard-mask]

WILDCARD MASK• Some IOS versions will also let you simply enter the subnet

mask. For example, you might enter the following:

• R2(config-router)#network 192.168.10.8 255.255.255.252

• However, the IOS will then convert the command to the wildcard mask format, as can be verified with the show run command:

• router eigrp 1

• network 172.16.0.0

• network 192.168.10.8 0.0.0.3

• auto-summary

BASIC EIGRP CONFIGURATIONVerifying EIGRP

• EIGRP routers must establish adjacencies with their neighbors before any updates can be sent or received

• Command used to view neighbor table and verify that EIGRP has established adjacencies with neighbors is

• show ip eigrp neighbors

SHOW IP EIGRP NEIGHBOR• H column - Lists the neighbors in the order they were learned.

• Address - The IP address of the neighbor.

• Interface - The local interface on which this Hello packet was received.

• Hold - The current hold time. Whenever a Hello packet is received, this value is reset to the maximum hold time for that interface and then counts down to zero. If zero is reached, the neighbor is considered "down".

• Uptime - Amount of time since this neighbor was added to the neighbor table.

• SRTT (Smooth Round Trip Timer) and RTO (Retransmit Interval) - Used by RTP to manage reliable EIGRP packets. SRTT and RTO are discussed further in CCNP courses.

• Queue Count - Should always be zero. If more than zero, then EIGRP packets are waiting to be sent. Queue count is discussed further in CCNP courses.

• Sequence Number - Used to track updates, queries, and reply packets. Sequence numbers are discussed further in CCNP courses.

EIGRP• The show ip protocols

command is also used to verify that EIGRP is enabled

• Remember, process IDs must match (AS #)

• Other rules also apply.

• WAN links have to be in the SAME subnet.

• PC’s and their gateway have to be in the same subnet!

BASIC EIGRP CONFIGURATIONExamining the Routing

Table

• The show ip route command is also used to verify EIGRP

• EIGRP routes are denoted in a routing table by the letter “D” - DUAL

• By default , EIGRP automatically summarizes routes at major network boundary

• You can do ‘no auto-summary’ like RIPv2..Sometimes you have to do this to make PINGS successful!

BASIC EIGRP CONFIGURATION• Introducing the Null0 Summary Route

–Null0 is not a physical interface

–In the routing table summary routes are sourced from Null0 Reason: routes are used for advertisement purposes

–EIGRP will automatically include a null0 summary route as child route when 2 conditions are met

At least one subnet is learned via EIGRP

Automatic summarization is enabled

BASIC EIGRP CONFIGURATION• R3’s routing table

shows that the 172.16.0.0/16 network is automatically summarized by R1 & R2

• R3 thinks these are equal-cost paths.

EIGRP METRIC CALCULATIONEIGRP Composite Metric & the K Values• EIGRP uses the following values in its composite

metric•-Bandwidth, delay, reliability, and load (only bandwidth and delay are actually used by default – see below)

• The composite metric used by EIGRP– formula used has values K1 K5

•K1 & K3 = 1•all other K values = 0

EIGRP METRIC CALCULATION

• Use the sh ip protocols command to verify the K values

EIGRP METRIC CALCULATION

EIGRP Metrics

• Use the show interfaces command to view metrics

• EIGRP Metrics•Bandwidth – EIGRP uses a static bandwidth to calculate metric

•Most serial interfaces use a default bandwidth value of 1.544Mbos (T1)

•Changing the bandwidth does not change the actual bandwidth!

EIGRP METRIC CALCULATION

EIGRP Metrics

• Delay is the defined as the measure of time it takes for a packet to traverse a route

•-it is a static value based on link type to which interface is connected

EIGRP METRIC CALCULATION – SKIM OVER• Reliability (not a default EIGRP metric)

•-A measure of the likelihood that a link will fail•-Measure dynamically & expressed as a fraction of 255• the higher the fraction the better the reliability

• Load (not a default EIGRP metric)– A number that reflects how much traffic is using a link– Number is determined dynamically and is expressed as a fraction of 255

The lower the fraction the less the load on the link

EIGRP METRIC CALCULATION - SKIM

Using the Bandwidth Command

• Modifying the interface bandwidth

•-Use the bandwidth command

•-Example

• Router(config-if)#bandwidth kilobits

• Verifying bandwidth

–Use the show interface command

• Note – bandwidth command does not change the link’s physical bandwidth

EIGRP METRIC CALCULATION

• The EIGRP metric can be determined by examining the

bandwidth delay

DUAL CONCEPTS

• The Diffusing Update Algorithm (DUAL) is used to prevent looping

DUAL CONCEPTS

• Successor – primary route

• The best least cost route to a destination found in the routing table

• Stored in the routing table and the topology table

• Feasible distance

• The lowest calculated metric along a path to a destination network

DUAL CONCEPTS

Feasible Successors, Feasibility Condition & Reported Distance

Feasible Successor

-This is a loop free backup route to same destination as successor route

- This route gets promoted to successor if the primary route fails!

DUAL CONCEPTS

• Reported distance (RD)

•-The metric that a router reports to a neighbor about its own cost to that network

Feasible Successors, Feasibility Condition & Reported Distance

DUAL CONCEPTS

• Feasibility Condition (FC)

•-Met when a neighbor’s RD is less than the local router’s FD to the same destination network

DUAL CONCEPTS

• Topology Table: Successor & Feasible Successor

• EIGRP Topology table

–Viewed using the show ip eigrp topology

command

Contents of table include:

– all successor routes

– all feasible successor

routes

•

EIGRP TOPOLOGY TABLE DISSECTED

P - the route will be in a stable mode.Route info – FD and route cost as advertised by neighbor routers is here!

Total metric for that network asadvertised by theEIGRP neighbor

TOPOLOGY TABLE

• The show ip eigrp topology all-links command shows all possible paths to a network including successors, feasible successors, and even those routes that are not feasible successors.

DUAL CONCEPTS

Topology Table: No Feasible Successor

• A feasible successor may not be present because the feasibility condition may not be met

•-In other words, the reported distance of the neighbor is greater than or equal to the current feasible distance

DUAL CONCEPTS - SKIM• Finite Sate Machine (FSM)

–An abstract machine that defines a set of possible states something can go through, what event causes those states and what events result form those states

–FSMs are used to describe how a device, computer program, or routing algorithm will react to a set of input events

–If FSM detects that a link to a network has gone down, it will search the topology table for a FS and/or query neighbors for a new route.

DUAL CONCEPTS - SKIM

Finite State Machines (FSM)

• To examine output from EIGRP’s finite state machine us the debug eigrp fsm command

MORE EIGRP CONFIGURATIONS - SKIM

The Null0 Summary Route

• By default, EIGRP uses the Null0 interface to discard any packets that match the parent route but do not match any of the child routes

• EIGRP automatically includes a null0 summary route as a child route whenever both of the following conditions exist

–One or subnets exists that was learned via EIGRP

–Automatic summarization is enabled

The Null0 Summary Route

MORE EIGRP CONFIGURATIONS

Disabling Automatic Summarization

• The auto-summary command permits EIGRP to automatically summarize at major network boundaries

• The no auto-summary command is used to disable automatic summarization

–This causes all EIGRP neighbors to send updates that will not be automatically summarized this will cause changes to appear in both

•-routing tables •-topology tables

MORE EIGRP CONFIGURATIONS - SKIMManual Summarization

• Manual summarization can include supernets

•Reason: EIGRP is a classless routing protocol & include subnet mask in update

• Command used to configure manual summarization

–Router(config-if)#ip summary-address eigrp  as-number network-address subnet-mask

MORE EIGRP CONFIGURATIONS - SKIM

• Configuring a summary route in EIGRP

MORE EIGRP CONFIGURATIONS – SKIM

EIGRP Default Routes

• “quad zero” static default route

•-Can be used with any currently supported routing protocol

•-Is usually configured on a router that is connected a network outside the EIGRP domain

• EIGRP & the “Quad zero” static default route

–Requires the use of the redistribute static command to disseminate default route in EIGRP updates

MORE EIGRP CONFIGURATIONS - SKIM

Fine-Tuning EIGRP

• EIGRP bandwidth utilization

•-By default, EIGRP uses only up to 50% of interface bandwidth for EIGRP information

•-The command to change the percentage of bandwidth used by EIGRP is

• Router(config-if)#ip bandwidth-percent eigrp as- number percent

MORE EIGRP CONFIGURATIONS - SKIM

• Configuring Hello Intervals and Hold Times•-Hello intervals and hold times are configurable on a per-interface basis•-The command to configure hello interval is• Router(config-if)#ip hello-interval eigrp as-number seconds

• Changing the hello interval also requires changing the hold time to a value greater than or equal to the hello interval

•-The command to configure hold time value is

• Router(config-if)#ip hold-time eigrp as-number seconds

SUMMARY• Choosing the best route

–After router has received all updates from directly connected neighbors, it can calculate its DUAL

1st metric is calculated for each route

2nd route with lowest metric is designated successor & is placed in routing table

3rd feasible successor is found

–Criteria for feasible successor: it must have lower reported distance to the destination than the installed route’s feasible distance

–Feasible routes are maintained in topology table

YEAH! Ch. 9 and all its glory…complete!

1.Study guide – 1. Pg. 389 – Matching2. Pg. 411 – Command reference

2.Labs1. 9-1 pg. 411- today/wednesday

3.Online test – take by Sunday, March 31, 2013- midnight4.Test - Wed, April 3, 2013